Remove Polo file manager

The program's repository has been archived, last release (1.8.3) has been 2 years ago, never out of beta and packaging has been dropped by most distribution that included it before.

README.md

@@ -441,7 +441,6 @@
 - [![Open-Source Software][OSS Icon]](https://github.com/GNOME/nautilus) [Nautilus](https://wiki.gnome.org/Apps/Files) - Nautilus (Files) is a file manager designed to fit the Gnome desktop design and behaviour, giving the user a simple way to navigate and manage its files.
 - [![Open-Source Software][OSS Icon]](https://github.com/linuxmint/nemo) [Nemo](https://github.com/linuxmint/nemo) - Nemo is the file manager for the Cinnamon desktop environment.
 - [![Open-Source Software][OSS Icon]](https://github.com/jarun/nnn) [nnn](https://github.com/jarun/nnn) - A very lightweight and fast terminal file browser with excellent desktop integration.
-- [![Open-Source Software][OSS Icon]](https://github.com/teejee2008/polo) [Polo](https://teejee2008.github.io/polo) - Polo is a modern, light-weight file manager for Linux with support for multiple panes and tabs; support for archives, and much more.
 - [![Open-Source Software][OSS Icon]](https://github.com/shundhammer/qdirstat) [QDirStat](https://github.com/shundhammer/qdirstat#ubuntu) - Qt-based directory statistics - KDirStat without any KDE, from the original KDirStat author.
 - [![Open-Source Software][OSS Icon]](https://github.com/ranger/ranger) [Ranger](https://ranger.github.io/) - Ranger is a console file manager with VI key bindings.
 - [![Open-Source Software][OSS Icon]](https://github.com/IgnorantGuru/spacefm) [SpaceFM](https://ignorantguru.github.io/spacefm/) - Multi-panel tabbed file and desktop manager with built-in VFS, udev- or HAL-based device manager, customisable menu system and bash-GTK integration.